A power amplifier is an indispensable part of a wireless base station, and efficiency of the power amplifier determines power consumption, a size, thermal design, and the like of the base station. Currently, in order to improve utilization efficiency of a frequency spectrum, modulation signals of different standards are used in wireless communications, such as orthogonal frequency division multiplexing (OFDM), Code Division Multiple Access (CDMA), and Time Division Multiple Access (TDMA) signals. According to specifications in related protocols, signals of these standards have different peak-to-average power ratios, for example, a peak-to-average power ratio of the OFDM is 10 to 12 dB. Signals with high peak-to-average ratios have higher requirements for a power amplifier in a base station.
In order to enable the power amplifier in the base station to undistortedly amplify these signals with high peak-to-average ratios, one method is a power back-off method, that is, the power amplifier works in a class-A or class-AB state; however, according to a feature of the power amplifier, the method causes a sharp decline in efficiency of the power amplifier, and in the case of a same output power, energy consumption of the base station is greatly increased. Another method is to combine a high-efficiency non-linear power amplifier with a linear digital technology such as digital predistortion (DPD). In this way, better efficiency of the power amplifier can be achieved, and linearity of the power amplifier can also meet a requirement in a related protocol. Currently, a Doherty technology is a high-efficiency mainstream power amplifier technology because of simple implementation and a low cost.
A conventional symmetrical Doherty power amplifying circuit achieves optimum efficiency at 6 dB back-off. In fact, a high peak-to-average power ratio as a trend becomes increasingly apparent in current and future communications systems, and in order to achieve higher efficiency in the case of signals with a higher peak-to-average power ratio, asymmetrical and multi-way Doherty technologies are applied more and more widely. For example, a typical 3-branch Doherty power amplifying circuit in the prior art generally has 3 power devices: 1 main power amplifier and 2 peak power amplifiers, where each of them is a separately encapsulated device.
However, problems exist in this power amplifying circuit. The main power amplifier accounts for most of the power consumption of the entire power amplifying circuit, and most of heat consumption is concentrated on one power device, namely the main power amplifier. This brings about some problems. First, heat concentration is adverse to heat dissipation of a system; and second, large heat consumption of the main power amplifier leads to deterioration in performance of the main power amplifier at a high temperature, and an excessively high junction temperature of a die of a chip reduces reliability of the main power amplifier.
Further, a conventional 3-branch Doherty power amplifying circuit uses three devices. A larger number of devices and a larger area of a module lead to an increase in costs of the entire module.